Hydraulic fracturing is performed through a work string that leads from the surface to the desired formation. At some point the work string goes through a seal point and could contain a bypass through that point so that the pressure at the formation can be determined by surface measurements of the annulus pressure that is communicated to the surface through the bypass of the work string that extends through the seal point. The seal point may be a packer or a seal bore. Hydraulic fracturing involves pumping proppant slurry into the wellbore through the work string to the desired formation. The work string terminates above or uphole from the formation being treated. The fluid is forced into the formation to fracture it. The proppant enters the formation to hold open the fissures created from pumping fluid under pressure into the formation to deposit the proppant.
The problem that arises occurs when the formation has what's called a sand out where flow into the formation declines dramatically because the proppant creates a barrier to further fluid progress into the formation. The conditions at the formation during fracturing are normally monitored by checking the annulus pressure at the surface. When the formation sands out the pressure at the formation increases generally because the pumping from the surface is with an engine driven multi-cylinder positive displacement pump. The problem with rising pressure at the formation is that the pressure also rises in the annulus going back to the surface. Going up the annulus there could be larger casing than at the formation that has a lower pressure rating. Alternatively the blowout preventer equipment can also have a lower pressure rating than casing that is closer to the formation being fractured. In those situations, the present invention provides a protection feature to prevent overpressure of these lower pressure rated components. These features and others will be better understood by those skilled in the art from a review of the detailed description and associated drawing that appear below while understanding that the full measure of the invention is found in the appended claims.